Evolution of microstructure in selected area deposition of diamond films by microwave plasma-enhanced chemical vapor deposition

Selected-area deposited (SAD) diamond films have been successfully grown on silicon substrates, using silicon-rich nitride (SiN) precoatings and negatively biased microwave plasma-enhanced chemical vapor deposition process. Lowering the total pressure in the CH4/H-2 mixture from 75 to 60 Torr significantly suppressed the nucleation of diamonds on Si substrate without modifying that on SiN substrate. A high selectivity (>200) SAD diamond film was thus obtained. The high etching rate on Si surface due to the hydrogen species is believed to be the main factor suppressing the diamond nucleation on Si surface. Scanning electron microscopy (SEM) indicates that the SAD and the quality of diamonds are optimized under the deposition conditions: 60 Torr total pressure, 2500 W microwave power, CH4-to-H-2 = 15:300 seem and - 120 V d.c. bias. In contrast, the diamonds can hardly grow on stoichiometric nitride (Si3N4) precoatings, which is ascribed to the insulating nature of these layers, blocking the application of a negative bias voltage. (C) 1998 Elsevier Science S.A.